Build LSK 3.14 kernel with android-toolchain

[Shawn Guo]

+ LAKML and more people.

On Mon, Dec 01, 2014 at 05:38:38PM +0100, Arnd Bergmann wrote:
> On Monday 01 December 2014 16:32:21 Shawn Guo wrote:
> > Is it a valid or supported use case to build LSK 3.14 kernel with
> > android-toolchain?  I can build a LSK 3.14 kernel with Linux toolchain
> > gcc-linaro-arm-none-eabi-4.9-2014.09, which boots fine on my board.
> > When I build the same kernel with
> > android-toolchain-eabi-4.9-2014.09-x86, the kernel can be built out
> > successfully, but it fails to boot on the board at very early stage
> > with only uncompressing message shown up like below.
> > 
> > Uncompressing Linux... done, booting the kernel.
> > 
> > And it's not a LSK 3.14 specific problem, I tried to build mainline
> > 3.10, 3.14 and 3.18-rc4 with the android-toolchain, and they all
> > failed to boot.
> > 
> > I need some help to understand if it's a valid use case at all, before
> > I try to looking into the problem.
> 
> I would expect it to work, it's probably a good idea to find out
> why it doesn't. For all I know 'arm-none-eabi' is actually /not/
> supported for building the kernel, since that doesn't use the Linux
> Linux variant of eabi, while 'arm-*-linux-gnueabi' or
> 'arm-*-linux-gnueabihf' is the default for Linux these days and
> 'arm-*-linux-android' should be compatible with that.

Okay.  Thanks for the info.  It seems that I should download
gcc-linaro-arm-linux-gnueabihf-4.9-2014.09 for comparison testing then.
Actually, in the very first testing I used arm-linux-gnueabi-gcc 4.7.3
shipped with Ubuntu 14.04.

> What is the
> exact target triplet you use in those two cases?

They are arm-none-eabi and arm-linux-androideabi.  And I also replaced
the first toolchain with arm-linux-gnueabi one, and got the same result.

> 
> A few things you could try:
> 
> - boot it in qemu using the vexpress or virt platform code, see if
>   the symptom is the same. If it is, attach gdb to the qemu gdbstub
>   to look at the contents of the _log_buf.
> 
> - Maybe debug_ll crashes, try disabling that
> 
> - Maybe debug_ll is disabled already, try enabling it to see if you
>   get more output.

I tracked it a little bit with debug_ll routine printch() and found it
dies at the first pr_info() call in arch/arm/kernel/setup.c:

	pr_info("Booting Linux on physical CPU 0x%x\n", mpidr);

And I spent some time to find out that the issue was introduced by
commit dad5451a322b (ARM: 7605/1: vmlinux.lds: Move .notes section
next to the rodata) since v3.8 release.  Reverting the commit helps me
to get a booting kernel that is built by arm-linux-androideabi
toolchain.  But I do not have the knowledge to understand what is
happening.

Shawn